Electricity control techniques for inverters are known in the art. U.S. Pat. No. 6,791,239 proposed by the Applicant is such an example. That technique focuses on the conventional inverter circuit and includes an individual pulse-width modulation (PWM) control unit, a driving unit, and a transformation unit to drive each discharge lamp (CCFL or EEFL). As the size of display panels increases gradually, the number of the discharge lamps also increases. The required electricity increases too. Hence the size of circuit board to accommodate the configuration of the PWM control unit, driving unit and transformation unit made according to the number of discharge lamps is larger, and circuit layout and production are more difficult. Illumination and electric field interference among the discharge lamps also increases. As a result, luminance uniformity suffers. While the aforesaid technique provides a solution, it mainly aims to provide, through a single PWM control unit, synchronous driving signals of the same phase and same frequency according to the driving units and transformation units that are required to drive the discharge lamps on the rear end. Thereby each driving unit, transformation unit and discharge lamp can be driven synchronously to achieve the uniform luminance.
However, with the size of the display panel increased constantly, the number of the discharge lamps increases even more. The circuit board has to be fabricated separately. Each separated circuit board includes a single PWM control unit to drive a plurality of driving units, transformation units and discharge lamps. The PWM control unit on each circuit board could encounter different frequency signals. For instance, U.S. patent publication No. 2004/0155601 A1 discloses a technique which arranges the discharge lamps in a staggered fashion. The problem of non-uniform luminance of the discharge lamps becomes more severe.